Electronic substrates have previously been formed with various alumina base ceramics including one material containing in approximate weight percent based on the starting batch formulation about 93% Al.sub.2 O.sub.3, 4.6% SiO.sub.2, 0.76% CaO, 0.8% MgO and 0.85% MoO.sub.3 which produced a final sintered article having a black color. Since higher alumina content ceramic materials were subsequently found to exhibit superior electrical and physical characteristics for electronic substrate applications, however, it would be desirable to further modify these ceramics without degrading the aforementioned superior characteristics to obtain still other benefits. Such higher performance electronic substrate alumina based ceramics are now frequently combined with integrated circuit components which either degrade in performance due to light exposure or are designed to be actuated with visible light. Accordingly, it would be desirable to reduce the light transmission in the ceramic substrate itself as a means of protecting any light-sensitive circuit components from exposure except when desired.